1. Field of the Invention
The present invention relates to a polishing apparatus for polishing a wafer or other workpiece held by a carrier using a rotating platen.
2. Description of the Related Art
In the past, as this type of polishing apparatus, there has been a chemical mechanical polishing (CMP) apparatus.
FIG. 10 is a sectional view of a CMP apparatus.
In FIG. 10, reference numeral 100 indicates a platen comprised of a disk having a polishing pad 101 adhered to its top surface.
The platen 100 is attached to the top surface of a rotary member 110 rotatably attached to a central shaft 111 through a bearing 112. This is designed to rotate integrally with the rotary member 110 by making the rotary member 110 rotate by a motor or other drive source 130.
In this CMP apparatus, a wafer 200 is placed as a workpiece on such a platen 100, the wafer 200 is pressed against it by a carrier 210, and the platen is made to rotate while supplying a polishing solution so as to polish the wafer 200.
Specifically, the carrier 210 presses the wafer 200 on the carrier 100 through a backing pad 211 attached to its bottom surface. The platen 100 and the carrier 210 are made to rotate in this state in the same direction at the same rotational speed. At this time, the carrier 210 is made to oscillate in the diametrical direction of the platen 100.
Further, in such a CMP apparatus, a laser sensor 300 is provided for measuring the state of polish of the wafer 200.
That is, a small diameter hole 120 is made passing through the polishing pad 101, the platen 100, and the rotary member 110. The laser sensor 300 is disposed under this hole 120. Due to this, when the hole 120 comes directly above the laser sensor 300 when the platen 100 is rotating, a laser beam is fired from the laser sensor 300 toward the hole 120 and measures the state of polish of the wafer 200 over the hole 120.
In such a polishing apparatus of the related art explained above, however, there were the following problems.
If the wafer 200 continues being polished, as shown in FIG. 11, the approximately center portion of the polishing pad 101 ends up becoming worn more than the inner peripheral portion or the outer peripheral portion.
That is, uneven wear occurs in the polishing pad 101. Each time, it is necessary to stop the CMP apparatus and dress the inner peripheral portion or outer peripheral portion to reduce them to the thickness of the center portion or to change the polishing pad 101. Therefore, the CMP apparatus had to be stopped for a long period and the operating rate of the apparatus was extremely poor.
Further, it is necessary to actuate the laser sensor 300 when the rotating hole 120 comes directly above the laser sensor 300, so the control of the timing is extremely difficult. In particular, the wafer 200 oscillates in the diametrical direction of the platen 100, so when the hole 120 arrives directly above the laser sensor 300, it is necessary to control the oscillation of the carrier 210 so that the center portion or peripheral edge portion of the wafer 200 was positioned directly above the hole 120. Control of this was difficult. Therefore, it was not possible to accurately measure the state of polish of the wafer 200.
Further, there were cases where laser measurement became no longer possible due to the polishing solution accumulating in the small hole 120.